Blade for rotary machines operated by high temperature media



Sept. 23, 1941. H. HOLZWARTH 2,256,479

BLADE FOR ROTARY MACHINES OPERATED BY HIGH TEMPERATURE MEDIA Filed March 17, 1939 3 Sheets-Sheet l l I I I I Q I I I I I I I J a i 4 6 em 72 l l l lbz zl fg INVENTOR l-hrrs HOLZ WIKTH ATTORNEYS f lufuTnn Sept. 23, 1941. H. HOLZWARTH 2,256,479

BLADE FOR ROTARY MACHINES OPERATED BY HIGH TEMPERATURE MEDIA Filed'March 17, 1939 3 Sheets-Sheet 2 INVENTOR H4: f/04z W/IETH BY 2 ATTORNEYS 1 Sep H. HOLZWARTH BLADE FOR ROTARY MACHINES OPERATED BY HIGH TEMPERATURE MEDIA Filed March 17, 1959 5 Sheets-Sheet 5 INVENTOR BY fi/a/vs f/oz. zwA/eTH E ATTORNEYS Patented Sept. 23, 1941 BLADE FOR ROTARY MACHINES OPERATED BY HIGH TEMPERATURE MEDIA Hans Holzwartb, Dusseldorf, Germany, assignor to Holzwarth Gas Turbine 00., San Francisco, Calif., a corporation of Delaware Application March 17, 1939, Serial No. 262,454 In Germany March 21, 1938 17 Claims.

- The present invention relates to the blading V More specifically, it is an object oi the invention to provide a blade having such a high heat conductivity from the free, outer tip to the base or. foot of the blade that adequate cooling of the blade may be accomplished by conducting a cooling agent in contact with substantially only the foot portion of the blade, and even when the cooling is of the hot type, that is, employs a. cooling agent at a .temperature considerably above room temperature, such as water at a temperature near its boiling point at superatmospheric pressure.

These and other objects of the invention, which will appear from the description herelnbelow, are realized in accordance with the preferred form of the invention by constructing the blade of an outer, heat-resisting shell made of a metal or alloy of high melting pointand capable of withstanding also the mechanical stresses, and an inner core of higher heat conductivity than the shell and in heat-conducting contact therewith, and relating the volumes of the outer shell and core in such a manner that the whole blade is adequately cooled, both at-the mechanically relat'. ely unstressed tip portions and at the highly stressed base'portion, even when a hot cooling agent is conducted in contact with the foot of the blade.

It is in general known to improve the cooling of blades, such as blades employed in combustion gas turbines, by inserting a core of greater heat conductivity within the blade, such as a core of copper or similar conducting material. It was, however, noted that as the cross-section of the core was increased in order to facilitate the withdrawal of heat, the temperature at the foot of the blade also gradually increased because the capacity of the blade footfor leading off heat did not increase to the same degree as the increase in the heat flow. Moreover, with increase in the size of the core, the shell of the blade necessarily became thinner, and as the strength of the blade dependedprimarily, if not entirely, upon the shell material, there appeared to be a limit to the size of the core beyond which the combination of increased blade foot temperature and reduced shell thickness and hence shell strength would operate to endanger the blade. especially blades exposed to both high temperatures and pressures and other stresses. This increase of the blade foot temperature was all the more serious as the greatest mechanical stresses occur at such place. A circular or conical form of core was accordingly employed, both .because of the convenience of manufacture of such core, and of the recess in the shell for receiving it by reason of their circular cross-section, and because such circular shape adequately limited the volume occupied by the core since the blade was of non-circular cross-section.

I have discovered the quite surprising fact that although with gradual increase in the volume of the core within the known limits, the blade tip temperature decreased at an approximately uniform rate for each unit increase in the core volume, at a certain more or less critical relationship of the volume of the shell to that of the core, the rate of blade tip temperature reduction for each unit increase of the core volume suddenly becomes enormously increased. I have found also that at approximately this same critical value the blade foot temperature suddenly begins to drop at a rate far greater than the rate of temperature increase in advance of such critical volume relationship for a unit increase in the core volume. Although, therefore, prior experience indicated that with increase of the core volume a more or less uniform decrease of the blade tip temperature accompanied by a more or less uniform increase of the blade foot temperature was to be expected, my investigations have shown that beyond a certain volume relationship between the shell and core, the blade foot temperature not only does not increase, but actually decreases rapidly and at a far higher rate than the previous rate of increase: while the blade tip temperature falls at a greatly accelerated rate.

According to the invention, therefore, the volume of the shell material is made approximately equal to or less than the above mentioned critical value. This critical ratio of shell volume to core volume is generally approximately equal to 4. This value is valid for all practical combinations of a highly heat-resistant shell material, that is, a material having a high strength at high temperatures, the shell acting as carrier for the core, and a highly heat-conducting core material, that is, a material having a heat conductivity -of the order of that of copper.

My invention thus makes it possible to build a stator or rotor blade with a. larger proportion of the cheaper, though mechanically weaker, core material such as copper, because the lower shell temperature signifies a stronger shell, the blade being thus able to withstand the stresses imposed thereon in operation in spite of the reduced mass of the shell material.

Two embodiments of the invention are illustrated by way of example on the accompanying drawings. In said drawings,

Fig. 1 shows the temperature curve at the blade tip in dependence upon the relationship of the space or volume occupied by the building material of higher heat resistance (shell material) to that occupied by the core wa Rx both with reference to the free blade length exposed to the working medium, while Fig. 2 represents in similar fashion the corresponding blade foot temperatures.

Fig. 3 illustrates a horizontal section through a guide or reversing blade constructed in accordance with the invention and taken along the lines III-III of Fig. 4.

Fig. 4 represents a vertical longitudinal section through the blade along the line IV-IV of Fig. 3.

Fig. 5 shows a section running vertically to the turbine wheel axis through a series of juxtaposed reversing blades of a conbustion gas turbine along the lines VV of Figs. 3 and 4.

Fig. 6 illustrates a modified form of mounting of the stator or reversing blade :1 while Fig. 7 shows a general schematic view, partly in section, of an explosion turbine plant having my improved blade construction embodied therein :[n the graph shown in Fig. 1, the proportion RWB x represents the abscissa, RwB corresponding to the space occupied by the working material of higher heat resistance, that is the outer shell, and RK the space occupied by the building material of higher heat conductivity or core. The temperatures ts in C., occurring at the blade tips, appear as ordinates. The ordinates drawn through the zero point of the co-ordinate system thus represent the temperature conditions in a blade which consists only of a good heat conductor, thus for example, only of copper; while the ordinate belonging to the abscissa point 00 represents the temperature course of a coreless blade, that is, of a blade which consists only of the building material of high heat resistance.

From the curve, shown in Fig. 1, it can be seen that I under the conditions between the abscissa values so and 4, a fall in the blade tip temperature occurs which at first proceeds approximately proportionally to the fall of the ratio whereas later with approach toward the value 4 tally. It now falls more steeply, that is, upon fall of the ratio below the limiting value 4, the blade tip temperatures drop so considerably that even with long blades subjected to high heat and temperature stresses, cooling of the blade foot in combination with cores of good heat conductors is sufilcient to protect the blade. More significant. however, is the temperature course it in the blade foot which is shown in Fig. 2 as dependent upon the ratio For while the blade foot temperatures between the abscissa values and 4 increase approximately proportionally to the decrease of the ratio, a little beyond, 1. e. below, the ratio value 4 a point of reversal in the curve occurs by reason of the peculiar and unexpected circumstance that from such point on, the temperatures at the blade foot fall precipitously in contrast to the previous slow temperature rise. From this it follows that to realize the favorable behavior of blades with foot and core cooling occurring between the values 4 and zero of the ratio the space occupied by the building material of higher heat resistance, referring to the free blade length exposed to the working medium, must be equal to about or be smaller than four times the core space, the amount of the material comprising the shell being of course greater than zero and being in fact suflicient to impart the necessary strength to the blade under the conditions of operation.

Figs. 3 to 5 illustrate such a blade constructed in accordance with the invention. It will be seen that the core I of copper or other equally highly heat-conducting material, in order to possess the necessary increased space relationship to the building material of higher heat resistance 2, no longer has a circular cross-section but rather one more nearly fitted to the blade cross-section perpendicular to the longitudinal blade axis. Thereby the di-iliculties in the manufacture of the copper core are indeed increased, and likewise of the formation of the cut-out in the (relatively) heat-resistant blade shell building material which receives it, and the fitting of the core and the production of the heat-conducting connection, but these difliculties in manufacture are more than compensated by the fact that the comparatively simple and safe blade foot cooling becomes applicable even in the case of the largest practicable blade lengths and increased heat or temperature stresses.

As shown in Fig. 4, the copper core I may be extended into the cooling space 3 which conducts the cooling agent destined for the blade cooling. The core extension 4 may be considerably widened with respect to the core I so that, particularly by the arrangement of grooves 5, cooling surfaces t of large surface area are created to an extent which affords unhindered heat conduction from the blade foot.

The blade is welded to the adjoining walls I of the cooling chamber 3, the welding joints being shown at 8 as reinforcing anchors for the blades. Water under particularly high pressure is suitable as cooling agent, the same being evaporated by the absorption of heat and yielding steam for the production of work. As explained below, the water may be heated to nearly the boiling point at high pressure in the cooling chambers and then caused to form steam upon reduction of the pressure.

In the embodiment shown in Fig. 6, the base 'of the blade is provided with slots at the sides thereof which are adapted to receive flanges or extensions la of the wall I constituting the support or part of the support of the blades. The flanges la act as anchoring members. The blades are inserted in a suitable break in the flanges and are slid therealong to their flnal position. In such position they may be welded to the flanges, and in order to fix the blades more firmly and at the same time provide additional conducting connections with the support, rings lb may be wedged or welded (in two or more sections) into the spaces between the blade and wall i above the flanges la, 1. e. inwardly radially in the case of stator blades.

With blade constructions of the type illustrated not only is the foot of the blade adequately cooled, but the exposed tip of the blade is maintained at a sufliciently low temperature to prevent injury thereto by the hot gases. This blade tip temperature is kept within safe limits, even in the case of long blades, by making the volume of the shell of the exposed portion of the blade no greater than about 4 times the volume of the core; thus the average cross-section of the shell in a plane perpendicular to the longitudinal axis of the blade may be made equal to about 4 times or less than 4 times the cross-section of the core. The core may be made of copper or other superior heat-conducting metal, copper being highly satisfactory as it conducts heat '7 times better than iron and about 11 times better than heat-resisting alloys; while the shell may be made of tungsten or tungsten-containing alloys or of other heat-resisting metals or alloys. When this volume relationship is observed, adequate cooling of the blade is insured in spite of the greater amount of heatconducted by the core; for as above explained, at and below the more or less critical volume relationship the additional amount of heat that is led off from the foot of the blade is greater than the additional amount of heat that flows to the foot, and the base of the blade thus actually falls in temperature.

It will accordingly be seen that whereas in the case of cores of circular cross-section the blade tip temperatures show only a proportional reduction with reduction of the value while maintaining the core circular, upon abandonment of the circular cross-section and further reduction of such ratio, it becomes possible to employ only blade foot cooling even in the case of blades of the largest practicable lengths and even when the maximum heat and mechanical stresses occur simultaneously and continuously.

The manner in which the heat of the cooling agent can be utilized for the production of working steam in an explosion turbine plant is shown by way of example in Fig. 7. One of a plurality of explosion chambers 9, working out of phase, is illustrated in Fig. '7, the chamber being provided with a scavenging air inlet valve ID, a fuel inlet member Ii and an additional valve I2 for air of higher pressure for eifecting atomization of a liquid fuel. The outlet valve l3 efiects discharge of the high temperature, high pressure gases generated by the explosion, brought about by the spark plugs ll, of an ignitable mixture of air and fuel in the chamber 9, the gases being directed by suitable nozzles to the first or impulse wheel. l5. From the latter they flow. preferably after intermediate equalization of their pressure,

to a continuously impinged rotor IS, the exhausted gases being discharged at II. The guide or stator blades 2 are in heat-conducting connection with the wall I forming part of a cooling jacket III which is connected by pipe it with an evaporator or steam separator 20. The separate steam of high pressure is withdrawn by the conduit 2| andconducted to a place of use, while the hot water is sucked by the pump 22 from the evaporator through the conduit 23 and recharged into the cooling space l8 by way of conduit 24. The water supply is replenished by a feed water pump 25 which is connected with the interior of the evaporator 20 by the pipe 26. The operation of the explosion chamber and its associated inlet and outlet mechanisms, the latter including also an auxiliary outlet valve |3a for the combustion gases of low pressure head, and also of its timing mechanism (not shown) is known and need not, therefore, be described herein.

The invention is of particular value for stator or reversing blades of combustion turbines, as such blades are continuously subjected to the action of the hot gases, whereas the rotor blades, in so far as the rotor is not a full admission rotor (i. e. impinged over 360) have an opportunity to cool outside the nozzle arc, such cooling being increased by ventilation. As already pointed out, the advantages of my invention are of particular significance in the case of hot" cooling. This hot cooling has the advantage that the average temperature of the cooling agent is increased. As the upper permissible cooling temperature is limited in view of the danger of steam formation, the average cooling agent temperature, on the other hand, being lower than the maximum temperature by half the difference between the inlet and outlet temperatures, the average cooling agent temperature is higher the lower this difference is. Maintaining the average cooling agent temperature high is important for the reason that the heat transfer to the wheel and to the blades falls considerably with increasing avarage cooling agent temperature. The heat losses to the wheel thus become smaller and the efliciency of the gas turbine becomes better the higher the average cooling agent temperature can be maintained, it being of advantage to employ the hot cooling and take into account the increased temperature stresses resulting therefrom. As, further, with guide or reversing blades a blade foot hot cooling is preferred because it is associated with special advantages, even though the temperature stresses would normally be increased, the temperature drop being considerably smaller than in a cooling with cold cooling agents, it will be clear that the improvement in the heat conduction accomi plished by the present invention is of striking importance.

The increase in the size of the core should not, of course, be carried to the point at which the strength of the blade and particularly of the shell is impaired. The shell will in all cases remain as the strength-providing element of the blade.

The term "shell as used herein is not to be understood as being limited to a member which completely encases the core. In certain blade constructions the "shell may be created only along the faces of the blade swept by the gases: thus at the farther side of the blades considered from the nozzles, the core may reach to the outer surface provided that it is sufliciently heatresisting.

I claim: 1. A blade for rotary machines operating with a medium of high temperature and comprising an outer body made of a material having a high strength at high temperatures but of relatively lower heat conductivity, and an inner core of relatively higher heat conductivity of the order of that of copper, the volume occupied by the carrying outer body, referred to the free blade portion exposed to the working medium, being approximately equal to, or, while maintaining the carrying capacity of the outer body, being less than, four times the space occupied by the core.

2. A blade according to claim 1, wherein the cross-section of the carrying outer body referred to the free blade length exposed to the working medium and in a plane perpendicular to the longitudinal axis of the blade, is approximately equal to, or smaller than, four times the crosssection occupied by the material of higher heat conductivity.

3. A rotary machine having a blade as defined in claim 1 and including, in combination, means providing a cooling chamber at the foot of the blade, and conduits for supplying a cooling agent to and withdrawing the same from said chamber, the heat conducting core being lengthened to extend into the cooling space and into contact with the cooling agent.

4. A rotary machine having a blade as defined in claim 1 and including, in combination, means providing a cooling chamber at the foot of the blade, and conduits for supplying a cooling agent to and withdrawing the same from said chamber. the heat conducting core being lengthened to extend into the cooling space and into contact with the cooling agent, the cross-section of the core extension lying in the path of the cooling agent being greater than that of the core within the exposed portion of the blade.

5. A rotary machine having a blade'as defined in claim 1 and including, in combination, means for conducting a hot liquid of lower temperature than the blade along the foot of the blade to effect cooling thereof.

6. In a rotary machine operating with a hot driving medium, such as combustion gases and the like, the combination of a series of blades, and a support for such blades, at least certain of said blades being composed of an outer shell made of a material having a high strength at high temperatures but of relatively lower heat conductivity, and a core of relatively higher heat conductivity of the order of that of copper, the volume occupied by the shell being no greater than about four times the volume occupied by the core in the exposed portion of the blade, said shell being made of such material and being so shaped that it is capable of transmitting to the support the forces imposed thereon during the operation of the machine.

7. A heat resisting blade for use in machines operating with a high temperature medium, comprising an outer shell made of a metallic material having a high strength at high temperatures, and a core made of a metal of greater heat conductivity than the material of the outer shell and of the order of that of copper, the volume of the material composing the shell being approximately equal to or less than four times the volume occupied by the core in the portion of the blade exposed to the hot medium.

8. In a rotary machine operating with a hot driving medium, such as combustion gases and the like, the combination of a series of blades, and a support for such blades, at least certain of said blades being composed of an outer shell made of a material having a high strength at high temperatures but of relatively lower heat conductivity, and a core of relatively higher heat conductivity by the order of that of copper, the volume occupied by the shell being no greater than about four times the volume occupied by the core, said shell being capable of transmitting to the support the forces imposed thereon during the operation of the machine, said support being provided with a cooling space at the base of the blade, and means for introducing a cooling agent into said space to eflect cooling of the blade by way of the foot thereof.

9. The combination set forth in claim 8, wherein the cooling agent is water, and including an evaporator, a conduit connecting the cooling space with the evaporator, a conduit for returning unevaporated water from the evaporator to the cooling space and means for withdrawing the separated steam from the evaporator.

10. The combination set forth in claim 8, wherein the core of the blade extends at the foot thereof beyond the shell and into the cooling space so as to be swept by the cooling agent.

11. The combination set forth in claim 8, wherein the core of the blade extends at the foot thereof beyond the shell and into the cooling space so as to be swept by the cooling agent, the core extension being provided with ribs to increase the heat transmitting surface thereof.

12. A blade as set forth in claim 1, wherein the core is made of copper.

13. The combination as defined in claim 6, wherein the shell is made of a heat-resisting metal alloy while the core is made of copper.

14. A blade as defined in claim 1, wherein the material of the core has at least about seven times the conductivity of that of the shell. 

